drillling seems only worth it when you are big and powerful and rolling in dosh.
small nations will have to rely on mercs sooner or later, or slacken recruitment standards for more manpower.
one could argue small nations could drill to get manpower from slacken standards, but i don't see point.
you will stop drilling fast, if an enemy invader wiped your troops within month of start of invading war, just because your drilling army has no morale...
hence, drilling is only safe/worth it if you can hide behind active forts....
which costs even more to do.